Functional amblyopia generally refers to a unilateral loss of visual acuity that is due neither to deficiencies in the optical components of the visual system nor to any apparent pathology within the visual pathways. Several lines of evidence are consistent with the prevalent belief that the locus of the deficiency is cortical. Earlier electroretinographic and psychophysical research appeared to support this viewpoint in that no abnormalities of retinal function were detected. However, for various methological considerations, it is unlikely that such studies would have detected any abnormalities that may exist at retinal levels. It is likely, for example, that the previously-used electroretinographic techniques were measuring activity originating primarily in the rod system and were therefore not sensitive for detecting possible deficiencies in macular function. Accordingly the aim of this project is to re-evaluate the integrity of retinal mechanisms in amblyopia through combined electroretinographic and psychophysical measurements of foveal function. The psychophysical experiments involve measurements of light and dark adaptation with various target sizes, thereby permitting a continuous assessment of the previously-reported anomalies in spatial summation and contrast threshold over a wide range of adaptation levels. This particular paradigm has the further advantage (viz. the application of Crawford's equivalent background transformation) of permitting a test of the hypothesis that the amblyopic central retina represents a simplified functional organization with respect to spatial information processing during adaptation. Measurements of the photopic ERG will be used in conjunction with the psychophysical results to determine whether such deficiencies as have been observed during dark-adaptation have their origin at a retinal level. The counterphased grating technique developed by Riggs and associates will be used to isolate the photopic ERG.